The present invention relates to improved apparatus for flash-smelting sulfidic ores and concentrates.
The process of flash-smelting, as is well known, entails injecting a sulfidic material into a furnace space with the aid of a stream of oxidizing gas, through appropriately designed burners, so that the injected feed "burns" while it is in a suspended state within the furnace chamber. The types of apparatus which have been designed for carrying out flash-smelting on a commercial scale can be divided for convenience into two general categories, namely furnaces which employ vertically disposed burners and those in which the burners are horizontally disposed. A well-known furnace design of the vertical burner type can be described as a generally U-shaped vessel consisting of a horizontal trough portion and two vertical limb portions. One or more burners are fitted at the upper extremity of one of the limb-portions and directed vertically downwards along the limb axis so that this particular limb defines the space within which burning of the feed takes place. The resulting liquid matte and slag collect as a pool within the trough portion of the furnace, while the other vertical limb of the furnace constitutes the offtake through which exhaust gases exit. In such apparatus the gas used to inject the feed is usually air or oxygen-enriched air, and additional burners are provided for injecting fuel to achieve and maintain the desired smelting temperature.
A furnace design of the second, i.e., horizontal burner, type is described in detail in the paper: "Oxygen flash smelting swings into commercial operation", Journal of Metals (1955) pp 742-750. This type of furnace, with which applicant has been associated for some time, is operated in a fully autogenous manner by using commercially pure (i.e., at least 95%) oxygen to inject the feed. Aside from obviating the need for additional fuel to maintain the smelting temperature, this method of operation offers the advantage of exhaust gases which are more concentrated in sulfur dioxide than would be the case if air were used instead of oxygen. The flue gases are therefore of a lower volume and also more amenable to recovery of the sulfur dioxide therefrom. The furnace construction, which is described in more detail hereinafter, is such as to define a chamber in the shape of a rectangular room with an arched ceiling. The burners are provided in the shorter of the side-walls, while the exhaust offtake is provided in the arched furnace-roof. In operation a pool of matte is formed in the furnace and tapped through an appropriate tap-hole in a long side-wall whereas a supernatant layer of slag is tapped as necessary through an appropriate tap-hole in one of the shorter side-walls, i.e. an end wall.
One important factor in the operation of the above-mentioned horizontal burner furnace has been the life of the refractory lining of the furnace. Gradual erosion of the refractory walls results in their eventual breakdown and necessitates expensive shut-down and rebuilding procedures. The erosion is most severe in the region of the side walls which in operation is contacted by the slag-matte interface. The erosion problem is aggravated by the tendency for an encrustation of magnetite to build up on the upper regions of the side walls. As a result of this combination of weakening of the lower region of the walls and build-up of magnetite on their higher regions, the walls eventually topple-over into the chamber. In order to offset this, the side walls have been built of graded thickness to provide substantially more refractory in the lower part thereof which houses the pool of matte and supernatant slag. Despite this, however, it has not hitherto been possible to operate the furnace for more than about 10-12 months without shutting it down to rebuild the lining.
It is an object of the present invention to provide a horizontal burner furnace of improved design wherein the life of the refractory lining is maximized.